Recommended oil for my 7.4
 

Hi I live in Michigan and am getting ready to fire up my old 1989 chaparral 7.4 Mercruiser. The boat has been sitting for 6+ years. I was gong to run a cheaper oil just for the start up then put in some Mobil 1. Any suggestions on what weight to use? I was thinking 20w-50

For a cheap oil i run delo 15 40 it has all the good stuff in it for flat tappet cams. Alot of over the road guys run it.

Rotella T.. Run it in everything..


John jr

No need for a overly viscous oil like a 20w-50. All that's going to gain you is poor start up
Lubrication and loss of horsepower. 10w-40 or a 15w-40 diesel oil works very well in a merc big block.

My buddy has an older Wellcraft with a 7.4 he runs the cheapest SAE 30wt he can find. Motor has over 700 hours on it and the only thing he has done to it literally is change the oil and a set of manifolds last year. The motor does have a hard life cause he's always boating with guys that have fast boats and often ends up doing some long tows across the bay at 30 mph...

99 cent WalMart oil or $12.99 a qt VTwin, you will never know the difference. Basic engine, doesn't matter.

Maybe in a stock Mercruiser 7.4, however this statement is false regarding racing engines.

If you will look more closely...."Basic engine, doesn't matter" and this is correct. No racing motor here.

I did, and as such clarified. I like to make sure clarification is made if someone else happens upon this thread. Oil is one of the least understood topics here on OSO. Fwiw

It is least understood because it does not matter in 90%+ of motors but everyone like to think it does.

Oh you know everyone has their brand of choice ;). It's like a religion.... I'm not going to agree upon 90%, however most applications do more than fine with readily available OTC motor oil. The technology utilized for additive systems used in passenger car oils these days makes some of the top 90's (true synthetics) look pathetic in comparison.

A flat tappet motor that has been sitting 6 years qualifies for the 10% it does matter on

i would use a oil that still has a lot of zink or add some zddp just because it has not been run in 6 years,jmo.if it was a 96 or newer i would not worry about the zink.

What he said................

I like bradpenn

Has lots of zinc for flat tappet cam usage.

Take this for what it's worth. Mobil/Exxon the largest oil company in the world and largest producer of base oils, states that high zinc levels thought to be mandatory in "flat tappet camshaft" engines is an overstated issue and that they side with manufacturers testing , and that most modern oils certified to current API standards( GF-5 for example) contain sufficient levels of ZDDP (zinc & phosphorus) to protect said cams after they have been properly broken in. I tend to believe what they say.

Just because a flat tappet cam fails later in life and wipes a lobe or mushrooms a lifter, we all believe it's the lack of ZDDP in the newer oils while none of us are chemists or tribologists..... Where's the proof guys?There's a thing called metallurgy that's likely to blame in these cases, not zinc & phosphorus. Most modern oils contain enough anti wear additives to keep a old flat tappet cam happy. However even the best oil can't rejuvenate some worn out turd of a cam. Just because an oil has high zinc & phosphorus doesn't make it superior, just as a group 5 base oil doesn't mean it's better than a group 4 base oil. It's the total formulation that makes a robust oil and matching it to the proper application.

http://www.bobistheoilguy.com/forums...Number=1049812

https://www.mobiloil.com/USA-English...d_Tappets.aspx

ZDDP is a great additive no doubt, however my belief is that this "more is better mentality" really has zero science to back it up. As a user how do you evaluate one oil formulation vs another. Answer: you trust a company to tell you what's best. Because if you don't have thousands of miles of UOA performed followed by teardowns with two oils in a fairly controlled environment then everything is just opinion.

And just to clarify, this isn't addressing any individual members directly. I'm not an oil guru by any stretch, however I have spent a good amount of time researching it since about 1996, and if possible like to provide some food for thought.

borgie,i am no oil expert but imo i can see no disadvantage to useing an oil with plenty of zddp.i use it in anything with a flat tappet camshaft and i have not had any lobe or lifter issues.unless someone can provide proof that i should not use oil with it i will continue to use it.

What cooking oil should I use in my wok for chicken stir fry? :gfight:

I've seen plenty of small and big block Chevy motors in both cars and boats wipe cam lobes back in the day when oils were supposedly "better" and had a ton of ZDDP in them.

Reminds me of my first car in high school, circa 1981. 76 Camaro with a 305. After I drove it hard doing donuts in the school parking lot, it eventually developed a lifter tick. I decided to rebuild the top end as my first real hot rod project. Didn't have the funds to swap in a 350 at the time, so we bought a replacement cam and lifters and sent the heads off for a valve job. I remember me and my buddy having to pull the lifters out by clamping vice grips around them with a block of wood and literally jumping on them to force the mushroomed lifters through the bores. Amazingly enough, apparently I didn't scuff the lifter bores enough to matter after our night of dancing on my engine. The thing actually ran pretty good with an aluminum intake and Holley 600 and a set of headers. Surprised a few 350s. Was still running strong when I sold it a few years later. Moral of the story - flat tappet cams are a reason that yesterday's engines only ran for 120K miles or so if you were lucky. Today's fully rollerized engines commonly go 250K+ due to the better valvetrain and less fuel dilution of the oil with fuel injection. Oh, and Borgie will also tell you - better oils that we have today. ;)

i have personally never had a lifter or a cam lobe go bad in any flat tappet cammed engine i have ever owned and i have had a ton of them.is it the oil i use or am i just a lucky guy?i can tell you that if it wasen,t for bad luck i would have no luck!

Every cam I have seen do this was due to lack of lube due to lack of oil changes or the backyarder mixing old used lifters after installing the legendary full race cam . I'm with Mike and have never had one of mine fail . Good oil , paying attention to the details upon assembly and break in or a combination of both ?

Ones I've seen were in good running engines with regular maintenance. I can only speculate that it was a bad core? Speaking to the lack of lube or maintenance and how it would affect a flat tappet cam, I can relate a personal story on a '79 Malibu I purchased in '85 as a college car. I knew the car had not been well maintained mechanically as the original owner was too cheap to replace a ripped wiper blade and the passenger side of the windshield was scored pretty bad. The price was right and the engine didn't smoke and checked out OK so I brought it home. The rotted out freeze plugs and the mess I found under the valve covers really spoke to just how poorly the car was maintained. Not shatting you I had to take a flat blade screwdriver and scrape/chisel "coked" junks of oil out from around all the valve springs, rockers, etc. How this engine was able to drain oil back down to the pan was beyond me. So, between running with oil that probably hadn't been changed in years and me then taking a stiff brush and kerosene and washing all around the springs and rockers with the heads still on the motor and then giving the motor a couple kerosene "flushes" you would think that would wipe the cam/lifters out. Nope. Ran like a top for the next 2 years and over 20K more miles. The engine was Chevy's flagship 267 cu in V-8 with a DuoJet. Flame thrower!!

Boy, those were some dark days in the world of automotive high performance, weren't they? I think that was close to the time that the T/A was about the hottest car you could buy, and even it was reduced to the crappy turbo 301 at some point. I really thought the high performance game was dead and buried at the time. Who could have guessed that 30 years later you could walk into a dealership and buy a 400+ HP fuel injected machine with a 6-speed manual?